Kinematics and Microphysics of Orographic Precipitation Associated with Different Background Precipitation of Typhoon Chanthu (2021)
Journal
Journal of the Atmospheric Sciences
Journal Volume
82
Journal Issue
12
Start Page
2737
End Page
2756
ISSN
0022-4928
1520-0469
Date Issued
2025-12
Author(s)
Hosokawa, Tsubaki
Abstract
This study used unique observations from ground-based traditional and polarimetric Doppler radars, a dense rain gauge network, and disdrometers to document the kinematic and microphysical characteristics of orographic precipitation over Da-Tun Mountain in northern Taiwan associated with Typhoon Chanthu (2021). Heavy precipitation occurred over Da-Tun, as it was influenced by strong low-level northerlies/northwesterlies of Chanthu’s circulations and the landfall of two distinct features of tropical cyclone (TC) background precipitation: outer rainband (OR) and weak stratiform (WS) precipitation. The OR precipitation was characterized by a deep layer of upward motion from the lower to upper troposphere, favoring the active production of ice crystals and subsequent aggregation and riming processes. The WS precipitation was characterized by nearly zero vertical velocities, leading to an inactive ice-phase growth process and thus smaller drop sizes and lower concentrations below the melting level. The precipitation enhancement over Da-Tun was indicated by an increase in all polarimetric variables toward the ground below 3.5 km (MSL) for both the OR and WS stages, highlighting the dominance of collision and coalescence processes, a manifestation of the collection of upslope-lifting-generated clouds (i.e., feeder clouds) by TC background precipitation (i.e., seeder clouds). The inherent microphysical properties of the OR and WS precipitation serving as seeder clouds, combined with ambient wind conditions, were found to play a critical role in determining the degree of orographic enhancement of precipitation and explaining the different locations of observed heaviest precipitation with respect to the mountain ridge between the two stages. SIGNIFICANCE STATEMENT: The understanding of the detailed processes contributing to tropical cyclone (TC)-generated orographic precipitation has been limited because of a lack of detailed observations over mountainous regions and the complicated nature of preexisting TC precipitation. With unique datasets available over Da-Tun in northern Taiwan, this study explores the kinematic and microphysical characteristics of the orographic enhancement of precipitation in different TC background precipitation features. Observational analyses provide robust evidence to support the importance of the seeder–feeder process for the occurrence of heavy precipitation over Da-Tun, in which the microphysical characteristics of TC background precipitation play a crucial role in influencing the degree of orographic enhancement of precipitation. The results provide important insights into the understanding of severe orographic rainfall associated with TCs.
Subjects
Cloud microphysics
Mesoscale processes
Orographic effects
Tropical cyclones
Publisher
American Meteorological Society
Type
journal article